TCAS: preventing mid-air collisions

Garfield Dean

ACAS Specialist at the EEC

In the early 1980s, following a mid-air collision over California, the United States government initiated the development of TCAS (Traffic alert and Collision Avoidance System). Skies were becoming more crowded and there was a need for a last-resort system to prevent mid-air collisions, should air traffic control or “see and avoid” fail. In the early 1990s, TCAS was first fitted on aircraft operating in US airspace and gradually implemented in the rest of the world. In 2000, TCAS became mandatory in Europe for larger passenger aircraft. Before TCAS was deployed in Europe, it was assessed at the EUROCONTROL Experimental Centre (EEC). Garfield Dean and the Safety Net team explain how this assessment was conducted and what the future brings.

How does TCAS avoid collisions?

Garfield Dean explains “TCAS detects nearby aircraft and if there is a risk of a collision it will tell the pilot how to adjust the aircraft’s altitude to avoid the collision.”

Why was it important to assess TCAS in Europe?

“Air traffic characteristics in the US and Europe are quite different, so TCAS had to be assessed in the context of the European air traffic management system. The main goal was to determine if TCAS was going to bring the foreseen safety benefits without introducing unacceptable risks.” replies Garfield Dean.

What work did the Experimental Centre do?

Garfield Dean answers “Since mid-air collisions are rare, the team had to simulate thousands of years of aircraft encounters in order to obtain statistically significant estimates of risk. Our analysis demonstrated that TCAS would make the airspace about three times safer. After deployment, monitoring-data collected at the EEC was used in an ongoing awareness creation campaign to improve pilot compliance with TCAS advisories.”

How will collision avoidance systems evolve in Europe in the coming years?

The Safety Net Team reply “In a couple of years we expect the arrival of an improved airborne collision avoidance system, ACAS X*, the successor of TCAS. Not only will ACAS X gradually replace TCAS on passenger aircraft but it will also provide collision avoidance benefits to new categories of airspace user, such as remotely piloted aircraft and general aviation. We are preparing for its arrival. An assessment, similar to the one conducted in the 1990s – but of much broader scope – is being conducted using recent radar data and state-of-the-art modelling tools.”